Electrical transmission wires, telephone wires and lighting fixtures are often supported on utility poles. Such poles must be capable of withstanding not only the columnar load applied by the weight of the objects supported thereon but also the bending load imposed by eccentric loading and by wind. As a general rule, wooden, concrete or steel poles have historically been used for this purpose. These poles are all heavy, and each presents some unique disadvantages.
Wooden poles, for example, are subject to rot--i.e.: decomposition from the action of bacteria or fungi--and pest attack--i.e.: wood borers and pecking fowl. Unfortunately, wooden poles are likely to rot at and below the ground surface which can result in a pole collapsing, or toppling, sometimes without warning. To help combat this type degradation the poles are typically treated with chemicals which are intended to prolong the useful life of the wooden pole. However, the chemical preservatives can leach out of the poles and contaminate the local ground water. Moreover, chemical preservatives are not permanent, and it is extremely difficult, if not impossible, effectively to treat wooden poles in the field.
Steel poles are subject to rust and therefore need constant attention and maintenance. The rust proofing compounds used can also have a deleterious effect on the environment. Even if the environmental problems could be solved, steel poles are heavy and are not easily manipulated. Moreover, steel poles are electrically conductive, and even though extreme care may be taken to insulate the electrical fixtures from the pole, routine storm damage can result in the pole becoming electrified. Finally, steel poles are an expensive inventory item.
Concrete poles are even heavier than steel poles. As a result, the expense of transporting and handling concrete utility poles can be excessive. They are, therefore, often constructed in fairly close proximity to the erection site. Concrete poles, like the aforementioned wooden and steel poles, are also subject to the ravages of the environment, particularly the freezing and thawing cycles which exist across massive geographic areas of the U.S.
Fiber reinforced plastic (FRP) poles have been suggested as an excellent replacement for wooden, steel and/or concrete poles because they are not as subject to the same deficiencies. For example, FRP composite poles provide a basic electrical insulation level that is greater than wooden, steel or concrete poles, and that basic electrical insulation level is maintained over the life of the FRP pole. Moreover, FRP utility poles provide an extremely favorable strength-to-weight ratio. FRP utility poles are generally comprised of several layers of fiber reinforced resin laminate. The fibers normally employed are glass, graphite, boron or other exotic materials, or combinations thereof, which have a Young's modulus on the order of at least about 10.times.10.sup.6 psi (6.9.times.10.sup.10 N/m.sup.2)--well sufficient to provide the hoop strength and stiffness necessary to prevent buckling and circular deformation of the shaft when under the loads typically imposed on utility poles.
FRP poles are also environmentally safe inasmuch as there is no leaching of chemicals into the soil. FRP poles, unlike their wooden counterparts do not require initial, or future, treatment with chemical preservatives. Conversely, the FRP composite utility poles possess an inherent resistance to attack from various chemicals that may be typically found in the soil.
However, the prior art FRP poles have proven to be too expensive. Typically, FRP poles are made by laying up resin coated fiberglass, or other high modulus strands, on a tapered mandrel. When the reinforcing filaments are wound on a tapered mandrel, the resulting tapered, tubular pole has a greater wall thickness at the tip portion of the pole than it does at the butt portion. Tubular FRP poles fabricated in this manner do possess high cantilever strength through the tip portion, where the wall thickness is greater and the outside diameter is smaller. However, in order to obtain tubular poles that have sufficient cantilever strength near the butt portion, excessive amounts of materials are amassed in the tip portion, thus unnecessarily increasing the cost and weight of the pole.